Motor vehicle disc brake systems generally utilize a disc brake rotor at each respective wheel (see FIG. 7). Each rotor, for example, generally includes two oppositely-facing annular friction surfaces which, during operation of the brakes, are engaged by two blocks of friction material (e.g., brake pads) that are moved towards one another into contact with the two friction surfaces so that frictional forces occur and slow the rotation of the rotor, and hence the wheel of the vehicle.
Accordingly, to slow and/or stop a vehicle, disc brake systems convert most of the kinetic energy of the vehicle to thermal energy primarily through the frictional forces between the brake pads and the rotors of the vehicle. A small amount of this kinetic energy, however, may also become vibrational energy within the brake system in both the brake pads (i.e., brake pad vibration) and rotors (i.e., rotor vibration). Thus, when damping of the brake system is low (which is often the case in the automotive industry), such vibration can result in radiation of high frequency sounds (e.g., over 1 kHz) from the brake system, otherwise referred to as squeal noise. In other words, squeal noise may be created by the dynamic instability of the brake system when the brake system linear vibration modes (i.e., pad and rotor vibrations) are placed closely in their resonant frequency range, and there is sufficient energy input to merge the modes, thereby creating an unstable complex system mode.
While this squeal noise does not indicate any functional imperfections or mechanical problems in the brake system, it may affect the driver's perception of the vehicle's quality and the integrity of the brake system itself, which may lead, for example, to unnecessary warranty claims and costs. Accordingly, various countermeasures may be employed to address squeal noise problems, including, for example: 1) separating the brake system linear modes to prevent their merging, and/or 2) reducing the energy input from the rotor/pad interaction.
Traditional solutions for addressing brake squeal noise have, however, been generally focused on the separation between pad and rotor modes, where pad modes that align with rotor modes are modified to shift their natural frequencies away from the rotor mode frequencies. In other words, traditional solutions for addressing brake squeal noise have generally been focused on brake pad vibration (i.e., brake pad free-free vibration modes), without addressing rotor vibration (i.e., brake rotor tension-compression natural vibration modes) or accounting for rotor mode contribution such as rotor tangential modes.
It may, therefore, be advantageous to provide a brake pad design that may reduce energy input from the pad to the rotor that could otherwise excite rotor tangential modes, thus providing a brake pad design that addresses and accounts for the rotor mode contribution to squeal noise.